The amount of information handled in information communication devices is steadily increasing and there is therefore a strong desire for a realization of a mass-storage system. In a HDD (hard disk drive) field, developments of various technologies including a perpendicular magnetic recording system are being made to realize high recoding density. Moreover, a discrete track medium and a bit-patterned medium are proposed in which a recording pattern is longitudinally isolated as a medium which can improve recording density and is also resistant to thermal decay at the same time, and it is essential to develop technologies for the production of these mediums.
It is only necessary that cells for magnetic recording be magnetically separated from each other to record one bit information by one cell as in the bit-patterned medium. In many mediums, a magnetic dot portion and a nonmagnetic dot portion are formed in the plane based on fine processing technologies.
Specifically, the magnetic recording layer on the substrate is isolated by applying semiconductor production technologies. After a patterning mask is formed on the upper part of the magnetic recording layer and a projections pattern is formed on the patterning mask, the formed pattern is transferred to the magnetic recording layer to obtain a magnetic recording medium having a recording pattern isolated by projections.
In the formation of projections on the mask pattern, a resist material generally used in the production of semiconductors is used to carry out any of the methods including a method in which a projections portion is selectively reformed by applying energy rays to obtain a pattern, a method in which a self-organizing film of an array of patterns differing in chemical nature is formed in the resist film by patterning, and a method in which a projections pattern is physically imprinted on the, resist film to carry out patterning.
There is, besides the above method, a method in which after projections is formed on a mask pattern, ions emitted with high energy are injected into the magnetic recording layer to selectively deactivate the magnetism of the pattern, thereby obtaining a medium with a recording pattern magnetically isolated via a non-recording region.
Here, in the case of scanning a medium with a magnetic head configured to perform reading/writing of a magnetic recording medium, difference in height between protrusion and recess parts is increased, giving rise to head crash if the mask pattern on the magnetic recording layer remains. Further, if the distance between the magnetic recording layer and the magnetic head is large, the signal S/N detectable by the magnetic head is small. This is why it is necessary to eliminate the mask pattern on the magnetic recording layer to decrease the difference in height between protrusion and recess parts after the patterning of magnetic recording layer and therefore a peelable layer is generally formed between the magnetic recording layer and the mask layer in an actual process.
As an example of a peeling process in a bit-patterned medium, a method is given in which a carbon peeling layer is removed by dry etching. In this case, however, this poses the problem that the magnetic recording layer is oxidized by oxygen which is etching gas, resulting in deterioration in the magnetic characteristics of the recording layer. Further, in the case where a huge residue having a size equal to or above the width of the projections pattern of the mask layer, the residue can be scarcely removed in the case of carrying out dry etching and tends to become a peeling defective position, giving rise to the problem that the position is left as a projection pattern on the medium. It is therefore difficult to obtain a medium ensuring longitudinal uniformity.
In the case of wet peeling on the contrary to the dry peeling, peeling progresses isotropically when a peeling solution is brought into contact with the peelable layer and therefore, a huge residue which is left in dry peeling can be peeled. Accordingly, an example is given in which a silicon-containing polymer is used as the peelable layer and this layer is wet-peeled by an organic solvent.
However, when the silicon-containing polymer is used for the peelable layer, heat energy is applied to the peelable layer by the formation of a mask layer or by etching to thereby promote a crosslinking reaction, resulting in significant hardening of the peelable layer. For this, the peelable layer is deteriorated in solubility in a solution, so that peeling defective parts are increased and also, long peeling time is required, leading to increase in process cost.